Methods for monitoring Ca²⁺ and ion channels in the lysosome

Lysosomes and lysosome-related organelles are emerging as intracellular Ca²⁺ stores and play important roles in a variety of membrane trafficking processes, including endocytosis, exocytosis, phagocytosis and autophagy. Impairment of lysosomal Ca²⁺ homeostasis and membrane trafficking has been implicated in many human diseases such as lysosomal storage diseases (LSDs), neurodegeneration, myopathy and cancer. Lysosomal membrane proteins, in particular ion channels, are crucial for lysosomal Ca²⁺ signaling. Compared with ion channels in the plasma membrane, lysosomal ion channels and their roles in lysosomal Ca²⁺ signaling are less understood, largely due to their intracellular localization and the lack of feasible functional assays directly applied to the native environment. Recent advances in biomedical methodology have made it possible to directly investigate ion channels in the lysosomal membrane. In this review, we provide a summary of the newly developed methods for monitoring lysosomal Ca²⁺ and ion channels, as well as the recent discovery of lysosomal ion channels and their significances in intracellular Ca²⁺ signaling. These new techniques will expand our research scope and our understanding of the nature of lysosomes and lysosome-related diseases.